In recent years there has been growing concern to produce energy-efficient lubricated components. Moreover, modern engine oil specifications require lubricants to demonstrate fuel efficiency in standardized engine tests. The thickness and frictional characteristics of thin lubricant films are known to affect the fuel economy properties of oils.
Thin-film friction is the friction generated from fluid, such as a lubricant, pushing between two surfaces, wherein the distance between the two surfaces is very narrow. It is known that different additives normally present in a lubricant composition form films of different thicknesses, which can have an effect on thin-film friction. Moreover, some additives have a narrow range of conditions wherein they provide reduced friction properties to a lubricant composition. Further, some additives, such as zinc dialkyl dithiophosphate (ZDDP) are known to increase thin-film friction.
However, it is also known that some additives are very expensive. And, the use of additional amounts of an additive to a lubricant composition to reduce thin-film friction can be quite costly to the manufacturer.
A major component of a lubricant composition can be the base oil, which is relatively inexpensive. Base oils are known and have been categorized under Groups I-V. The base oils are placed in a given Group based upon their % saturates, % sulfur content, and viscosity index. For example, all Group II base oils have greater than 90% saturates, less than 0.03% sulfur, and a viscosity index ranging from ≧80 to ≦120. However, the proportions of aromatics, paraffinics, and naphthenics can vary substantially in the Group II base oils. It is known that the difference in these proportions can affect the properties of a lubricant composition, such as oxidative stability.
What is needed is a lubricant composition that is inexpensive and can provide at least one of reduced thin-film friction and increased fuel economy.